/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#ifndef _THRIFT_CONCURRENCY_THREADMANAGER_H_
#define _THRIFT_CONCURRENCY_THREADMANAGER_H_ 1

#include <boost/shared_ptr.hpp>
#include <thrift/cxxfunctional.h>
#include <sys/types.h>
#include <thrift/concurrency/Thread.h>

namespace apache
{
namespace thrift
{
namespace concurrency
{

/**
 * Thread Pool Manager and related classes
 *
 * @version $Id:$
 */
class ThreadManager;

/**
 * ThreadManager class
 *
 * This class manages a pool of threads. It uses a ThreadFactory to create
 * threads. It never actually creates or destroys worker threads, rather
 * It maintains statistics on number of idle threads, number of active threads,
 * task backlog, and average wait and service times and informs the PoolPolicy
 * object bound to instances of this manager of interesting transitions. It is
 * then up the PoolPolicy object to decide if the thread pool size needs to be
 * adjusted and call this object addWorker and removeWorker methods to make
 * changes.
 *
 * This design allows different policy implementations to used this code to
 * handle basic worker thread management and worker task execution and focus on
 * policy issues. The simplest policy, StaticPolicy, does nothing other than
 * create a fixed number of threads.
 */
class ThreadManager
{

protected:
    ThreadManager() {}

public:
    class Task;
    typedef apache::thrift::stdcxx::function<void(boost::shared_ptr<Runnable>)> ExpireCallback;

    virtual ~ThreadManager() {}

    /**
     * Starts the thread manager. Verifies all attributes have been properly
     * initialized, then allocates necessary resources to begin operation
     */
    virtual void start() = 0;

    /**
     * Stops the thread manager. Aborts all remaining unprocessed task, shuts
     * down all created worker threads, and realeases all allocated resources.
     * This method blocks for all worker threads to complete, thus it can
     * potentially block forever if a worker thread is running a task that
     * won't terminate.
     */
    virtual void stop() = 0;

    /**
     * Joins the thread manager. This is the same as stop, except that it will
     * block until all the workers have finished their work. At that point
     * the ThreadManager will transition into the STOPPED state.
     */
    virtual void join() = 0;

    enum STATE
    {
        UNINITIALIZED,
        STARTING,
        STARTED,
        JOINING,
        STOPPING,
        STOPPED
    };

    virtual STATE state() const = 0;

    virtual boost::shared_ptr<ThreadFactory> threadFactory() const = 0;

    virtual void threadFactory(boost::shared_ptr<ThreadFactory> value) = 0;

    virtual void addWorker(size_t value = 1) = 0;

    virtual void removeWorker(size_t value = 1) = 0;

    /**
     * Gets the current number of idle worker threads
     */
    virtual size_t idleWorkerCount() const = 0;

    /**
     * Gets the current number of total worker threads
     */
    virtual size_t workerCount() const = 0;

    /**
     * Gets the current number of pending tasks
     */
    virtual size_t pendingTaskCount() const  = 0;

    /**
     * Gets the current number of pending and executing tasks
     */
    virtual size_t totalTaskCount() const = 0;

    /**
     * Gets the maximum pending task count.  0 indicates no maximum
     */
    virtual size_t pendingTaskCountMax() const = 0;

    /**
     * Gets the number of tasks which have been expired without being run.
     */
    virtual size_t expiredTaskCount() = 0;

    /**
     * Adds a task to be executed at some time in the future by a worker thread.
     *
     * This method will block if pendingTaskCountMax() in not zero and pendingTaskCount()
     * is greater than or equalt to pendingTaskCountMax().  If this method is called in the
     * context of a ThreadManager worker thread it will throw a
     * TooManyPendingTasksException
     *
     * @param task  The task to queue for execution
     *
     * @param timeout Time to wait in milliseconds to add a task when a pending-task-count
     * is specified. Specific cases:
     * timeout = 0  : Wait forever to queue task.
     * timeout = -1 : Return immediately if pending task count exceeds specified max
     * @param expiration when nonzero, the number of milliseconds the task is valid
     * to be run; if exceeded, the task will be dropped off the queue and not run.
     *
     * @throws TooManyPendingTasksException Pending task count exceeds max pending task count
     */
    virtual void add(boost::shared_ptr<Runnable>task,
                     int64_t timeout = 0LL,
                     int64_t expiration = 0LL) = 0;

    /**
     * Removes a pending task
     */
    virtual void remove(boost::shared_ptr<Runnable> task) = 0;

    /**
     * Remove the next pending task which would be run.
     *
     * @return the task removed.
     */
    virtual boost::shared_ptr<Runnable> removeNextPending() = 0;

    /**
     * Remove tasks from front of task queue that have expired.
     */
    virtual void removeExpiredTasks() = 0;

    /**
     * Set a callback to be called when a task is expired and not run.
     *
     * @param expireCallback a function called with the shared_ptr<Runnable> for
     * the expired task.
     */
    virtual void setExpireCallback(ExpireCallback expireCallback) = 0;

    static boost::shared_ptr<ThreadManager> newThreadManager();

    /**
     * Creates a simple thread manager the uses count number of worker threads and has
     * a pendingTaskCountMax maximum pending tasks. The default, 0, specified no limit
     * on pending tasks
     */
    static boost::shared_ptr<ThreadManager> newSimpleThreadManager(size_t count = 4, size_t pendingTaskCountMax = 0);

    class Task;

    class Worker;

    class Impl;
};

}
}
} // apache::thrift::concurrency

#endif // #ifndef _THRIFT_CONCURRENCY_THREADMANAGER_H_
